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with ether and chloroform the effect was slight or lacking. In all cases the reversibility of the change induced by the anaesthetic was proved by subjecting the eggs to a second osmotic test about twenty minutes. after returning to sea-water; the tested eggs then showed the typical rapid collapse and crenation, and eggs left undisturbed after the return to sea-water continued their development to larval stages.

It is clear that the anaesthetic modifies the permeability of the membrane to water as well as its general stability or resistance to alteration.32 Just how this effect is produced remains for the present problematical. The anaesthetic may promote the continuity of the nonaqueous or lipoid phase of the protoplasmic emulsion at the boundarysurface of the cell, possibly in the manner suggested by Clowes;33 or it is possible that by dissolving in this phase it may increase the relative volume occupied by the colloidal particles of lipoid and hence decrease the relative volume of the aqueous phase of the emulsion, thus making the latter a more effective barrier to the passage of water (and presumably to water-soluble substances also). In all probability the total effect depends upon a combination of several distinct actions, in which metabolic factors also enter. The plasma-membrane is undoubtedly the seat of an active metabolism of an oxidative type, and substances produced, altered or destroyed in this metabolism must influence its physical and other properties.

SUMMARY

1. Fertilized eggs of Arbacia and Echinarachnius shrink rapidly and undergo crenation in hypertonic sea-water or van't Hoff's solution (of 30 to 40 atmospheres O.P.); unfertilized eggs shrink slowly in the same solutions and remain round. The relative rates of swelling in dilute sea-water are similar. Fertilization thus results in a marked increase in the permeability of the plasma-membrane (the semi-permeable surface-layer of protoplasm) to water.

2. Artificial formation of fertilization-membranes by butyric acid causes similar though more variable effects in Arbacia eggs. Eggs with

32 It has been mentioned that anaesthetized uncleaved eggs show greater resistance than normal eggs to the permeability-increasing action of pure isotonic salt-solutions; this fact explains why the activating effect of such solutions is prevented by anaesthetics, since activation involves increase of permeability; similarly with the inhibiting action of anaesthetics on cleavage which also is associated with a change in the plasma-membrane.

33 Clowes: Journ. Phys. Chem., 1916, xx, 407.

well-separated membrane exhibit a well-marked increase of permeability like that of sperm-fertilized eggs; when membrane-formation is imperfect or lacking the increase of permeability is less marked or may not be evident.

3. The change of permeability is a gradual process, beginning between two and four minutes after insemination and reaching an approximate final stage in about twenty minutes (at 20 to 22°).

4. The change of permeability is arrested or retarded reversibly by potassium cyanide in concentrations of M/100 to м/400; concentrations of м/800 and lower are ineffective. This change is much more resistant to cyanide than cleavage.

5. Anaesthetics (chloral hydrate, alcohols, urethane, ether) also prevent the increase of permeability, in concentrations which are similar to but in some cases higher than the concentrations arresting cleavage in the same eggs. The effect is readily reversible. A direct influence of anaesthetics upon the permeability to water is thus demonstrable. Eggs which have undergone the normal increase of permeability following fertilization also show a reversible decrease of permeability to water in solutions of certain anaesthetics (chloral hydrate, alcohols, urethane).

AN EXPERIMENTAL STUDY OF ALTERNATING GROWTH

AND SUPPRESSION OF GROWTH IN THE ALBINO MOUSE, WITH SPECIAL REFERENCE TO THE ECONOMY OF FOOD CONSUMPTION

HELEN B. THOMPSON AND LAFAYETTE B. MENDEL

From the Sheffield Laboratory of Physiological Chemistry of Yale University, New Haven, and the Connecticut College for Women

Received for publication January 18, 1917

INTRODUCTION

Although much is known regarding the conditions under which growth may be retarded or promoted, the food consumption in relation to growth has not been studied extensively. For this reason it was thought that an investigation of the economy of food in alternating periods of growth and suppression of growth in an animal for which the diet could be controlled with accuracy would prove to be of value. The white mouse was chosen for study in the present research. It was planned to make the comparative food intake during normal, suppressed and accelerated growth the basis for a consideration of the economy of food in growth as a contribution to some of the problems of animal production. Statistics are herewith offered for the average daily food requirement, together with the curves of normal growth for both male and female mice from the age of weaning, 22 days, to the age at which average adult weight is reached, 62 days. The food consumption per day of normally growing mice has been estimated for varying body weights of from 7 to 25 grams. The daily food requirement for maintaining body weight both in an initial suppression and in repeated suppressions of growth has been compared with that for normal growth. The total food required to complete growth during a period of refeeding after suppression of growth has been compared with the food consumption of controls making the same growth from

1 This study was aided by a grant from the Elizabeth Thompson Science Fund. The data are taken from the dissertation presented by Helen B. Thompson for the degree of Ph.D., Yale University, 1917.

the same initial weight. The total food consumed during the period of suppression of growth and the following period of refeeding has also been compared with the total consumption of the control animals for an equal number of days at corresponding ages.

It was hoped by the study indicated above to test the following points: the relation of the food intake to normal growth at different ages and at varying body weights; the food requirement per day in suppressed growth for varying periods and for successive suppressions; the economy of food in accelerated growth; the cost, in total food, of maintenance and growth when growth is completed after one or more suppressions.

PLAN OF INVESTIGATION

The mice were placed, when 20 to 22 days of age, in individual cages made of galvanized wire cloth. Absorbent paper covered with a mat of galvanized fly screen wire was used to line the bottom of the cage. The entire cage was cleaned at least once a week. Every day, while each mouse was being weighed before feeding, its cage was taken apart and the uneaten food collected, the feces removed and clean paper supplied if needed. Food and water cups were sterilized by boiling twice a week. Water cups were washed every day.

As a fairly high uniform temperature has been shown to be important in maintaining underfed animals in good health, the room temperature was kept day and night between 70° and 85°F.

The food was made up from the formula employed by Wheeler ('13) and later by Judson ('16). This ration was selected because it had been demonstrated by Osborne and Mendel in feeding rats that a paste is desirable from the standpoint of economy in handling. It was essential to have a food that could be easily weighed out and from which refuse and scattered remnants could be accurately collected. The food was made up as follows:

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2 Dissertation presented by S. E. Judson for the degree of Ph.D., Yale University, 1916. See Mendel and Judson: Proceedings of the National Academy of Sciences, 1916, ii, 692.

Salt mixture3.

Butter fat..

32

By analysis of a mixed sample of food prepared at several different times the composition was found to be:

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Food was mixed fresh two or three times a week in quantities of 300 to 400 grams. It kept well without apparent fermentation or mold formation. Daily rations were weighed in grams and tenth grams; residues in milligrams.

In the early experiments it was noticed that a number of the mice ate irregularly and grew slowly. Those that did eat regularly grew at the rate described by Judson. As abnormally slow growth may indicate a low plane of nutrition brought about through failure of appetite as well as a deficiency in any food constituent, a source of vitamine in the form of 2 per cent of yeast was added to the diet without otherwise modifying the food mixture. This change was made for both the control mice and those maintained at constant weight. All animals ate much more regularly after the inclusion of yeast in the diet.

The yeast was "Torula" from the Hinckel Brewery Company, Albany, N. Y., which states that "Torula" contains on an average:

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With 2 grams of yeast added to 100 grams of food the estimated composition of the mixture then became:

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(From Osborne and Mendel: Carnegie Inst. of Washington, 1911, Publ. 156, I, 32.)

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